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    SubjectRe: [PATCH 3/7] openrisc: restore call-saved regs on sigreturn
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    On 09/16/2016 04:43 PM, Stafford Horne wrote:
    > From: Jonas Bonn <jonas@southpole.se>
    >
    > Return to userspace via _resume_userspace instead of via syscall return
    > path for the rt_sigreturn syscall.
    >
    > I'll rework this comment more later, but this patch needs testing.

    This whole patch was reworked later... what happened to that work? I
    recall it being posted for testing without feedback...

    In any case, the patch comment needs cleaning up.

    /Jonas

    >
    > Old comment from previous patch:
    >
    > The sigreturn syscall is more like a context switch than a function call;
    > it entails a return from one context (the signal handler) to another
    > (the process in question). For a context switch like this there are
    > effectively no call-saved regs that remain constant across the transition.
    >
    > This patch restores the call-saved regs from pt_regs before returning from
    > the syscall, effectively restoring the context that the process had before
    > being interrupted by the signal handler. Restoring the call-saved regs
    > in this way allows us to return to userspace via the usual syscall fast
    > path.
    >
    > Reported-by: Sebastian Macke <sebastian@macke.de>
    > Signed-off-by: Jonas Bonn <jonas@southpole.se>
    > Signed-off-by: Stafford Horne <shorne@gmail.com>
    > ---
    > arch/openrisc/kernel/entry.S | 10 +++++++++-
    > 1 file changed, 9 insertions(+), 1 deletion(-)
    >
    > diff --git a/arch/openrisc/kernel/entry.S b/arch/openrisc/kernel/entry.S
    > index fec8bf9..572d223 100644
    > --- a/arch/openrisc/kernel/entry.S
    > +++ b/arch/openrisc/kernel/entry.S
    > @@ -1101,8 +1101,16 @@ ENTRY(__sys_fork)
    > l.addi r3,r1,0
    >
    > ENTRY(sys_rt_sigreturn)
    > - l.j _sys_rt_sigreturn
    > + l.jal _sys_rt_sigreturn
    > l.addi r3,r1,0
    > + l.sfne r30,r0
    > + l.bnf _no_syscall_trace
    > + l.nop
    > + l.jal do_syscall_trace_leave
    > + l.addi r3,r1,0
    > +_no_syscall_trace:
    > + l.j _resume_userspace
    > + l.nop
    >
    > /* This is a catch-all syscall for atomic instructions for the OpenRISC 1000.
    > * The functions takes a variable number of parameters depending on which

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